Jurassic volcanic rocks in southeastern Arizona provide an opportunity to study the paleomagnetism of an autochthonous segment of the Mesozoic Cordilleran magmatic arc. The Corral Canyon sequence in the Patagonia Mountains is a 650 meter thick homoclinal sequence consisting of interbedded volcaniclastic red-beds, welded ash-flow tuff, and lavas. Rb/Sr isotopic analysis of eight whole rock tuff samples yields an isochron age of 171 ± 3 Ma. Welded tuffs in the Corral Canyon sequence possess a stable, primary magnetization carried in both magnetite and hematite that defines a paleomagnetic pole at 61.8°N, 116.0°E, alpha₉₅= 6.2°. This pole is considered to be a reliable Middle Jurassic reference pole for cratonic North America. Paleomagnetic study of the Canelo Hills volcanics welded tuff member also yields a stable, primary magnetization throughout a stratigraphic thickness of 600 meters. However, results from this formation are enigmatic and the mean pole is discordant with respect to Middle Jurassic reference poles. Various aspects of the paleomagnetic data indicate that discordance of the Canelo Hills volcanics pole is probably due to acquisition of remanent magnetization during a period of non-dipole behavior of the geomagnetic field. Dispersion of paleomagnetic directions suggests that the welded tuff member represents at most two cooling units and can be interpreted as a caldera-fill sequence. A revised Jurassic APW path differs significantly from available paths and has important implications for North American plate motion and paleolatitude. The spatio-temporal progression of reliable Jurassic paleopoles, in conjunction with Triassic and Early Cretaceous poles, is well described by paleomagnetic Euler pole analysis. The APW path is divided into three tracks, separated by two cusps. These cusps represent changes in the direction of North American absolute plate motion and can be correlated with global plate motion and intraplate deformation events at approximately 200-210 Ma and 150 Ma. Finally, the APW path presented herein predicts more southerly Late Triassic and Jurassic paleolatitudes for North America than have been suggested by previous authors. Using revised reference poles, there are no inclination anomalies within paleomagnetic data from Late Triassic and Early Jurassic rocks of Stikinia and Quesnellia (B.C., Canada).

Fossil bearing continental deposits, the Gila Conglomerate, of the Safford and Duncan Basins, Arizona were correlated with the magnetic polarity time scale by means of magnetostratigraphy and biochronology of mammalian fossils. Within the Safford Basin, the Bear Springs section with a middle Blancan fauna is correlated with the lower or upper Gauss chron; the 111 Ranch section with a middle to late Blancan fauna is correlated with the upper Gauss to early Matuyama chrons; and the San Simon Power Line section with probably a latest Blancan fauna is correlated with the early Matuyama chron. In the Duncan Basin, the Duncan section with a middle Blancan fauna is correlated with the middle Gauss chron; the Pearson Mesa section with a middle Blancan fauna is correlated with the Upper Gauss chron; and the Country Club section with a middle Blancan fauna is correlated with the latest Gilbert to early Gauss chrons or from the middle Gauss to the earliest Matuyama chrons. A late Blancan fauna is not recognized in the Duncan Basin at least within the study area, whereas the Gila Conglomerate in the Safford Basin includes deposits and fauna of the latest Blancan (latest Pliocene) age. A minimum of 37 taxa of small mammals are recognized among the approximately 1,600 specimens from the Gila Conglomerate of the Safford and Duncan Basins. Three new rodent species are described; they are Pappogeomys (Cratogeomys) sansimonensis, new species; Reithrodontomys galushai, new species; and Repomys arizonensis, new species. One new combination of genus and species, Hypolague virginiae, is described. In the Safford Basin, a minimum of 26 small mammal taxa are now recognized in the 111 Ranch fauna, of which three genera (Dipodomys, Peromyscus, and Repomys) are new records to the fauna; a minimum of 6 taxa of small mammals are recognized and described for the first time in the San Simon Power Line fauna. In the Duncan Basin, a minimum of 15 small mammal taxa are recognized and described for the first time.

Cenozoic deposits in intermontane basins in the upper Gila River basin have been collectively included in the Gila conglomerate of Gilbert and Ransome. Re-examination of type-section areas shows that the term is unsatisfactory because it includes a substantial proportion of deposits other than conglomerates; it suggests that deposits in separate basins are identical; its use masks sequences of alluvial deposits within individual basins and relationships of deposits between basins; and it oversimplifies a complex Cenozoic history. It is suggested that the term Gila conglomerate be abandoned. The deposits, in the many basins, which heretofore may have been included in the Gila conglomerate, can be separated into two major divisions which may in turn be subdivided into mappable rock units. In each structural trough the upper units are characterized by: (1) Truncation by the highest pediment surfaces; (2) depositional or normal-fault contact with adjacent mountain areas whose composition the deposits reflect; (3) size-gradation relationships that suggest deposition within the boundaries of the present structural troughs; and (4) lack of mineralization. Limited fossil evidence suggests that deposition occurred during Pliocene to Pleistocene (Kansan) time. The lower units crop out in areas of deep dissection or structural uplift. They may be in fault contact with the upper units, underlie them unconformably, or grade into them. The lower units are characterized by: (1) Texture and composition that suggest deposition in basins other than those reflected by the present topography; (2) thrusting or normal faulting more complex than that associated with the upper units; (3) local mineralization; and (4) shallow intrusion. Limited fossil evidence sug gests a Miocene age for some of the older of the lower units, The alluvial deposits in individual basins in this area are amenable to stratigraphic analysis by standard procedures for describing rock units Correlations within or between basins should be on the basis of proper fossil or stratigraphic evidence and should be limited to the particular units involved and not expanded to include all the alluvial deposits in the areas concerned.

A stratigraphic radiocarbon study at the Wilicox Playa and vicinity in Cochise County, southeastern Arizona has revealed a sedimentary sequence reflecting the lake level chronology of ancient Lake Cochise. The lower green clay was deposited in a lake at least 30 miles long from before 30,000 years ago until about 13,000 years ago. A marl formation which began depositing about 25,000 years ago and continued until the lake diminishe to about its present state 13,000 years ago, indicates a warm, moist climate at that time. The period from 13,000 B.P. (before present) and 11,000 B.P. was one of alluvial deposition north of the playa and channel cutting east of the playa. An upper green clay, 6 to 8 inches thick, represented the final phase of Lake Cochise, lasting from 11,500 B.P. until 10,500 B.P. A thin marl layer was deposited during this phase, indicating warm moist conditions again. The lake rapidly receded, some playa sediments deflated from the surface, and dunes formed north of the playa. Preliminary studies of two playas near Lordsburg, New Mexico and one at the San Augustin Plains, New Mexico, indicate these fluctuations were responding to a general climate change rather than isolated tectonic disturbances. The climate chronology concluded from this study is consistent with known climatic variations in the world.

Post-Miocene fluvial and lacustrine units coristitute the valley fill of the San Pedro Valley, near Redington, Arizona. These sediments are relatively flat lying units deposited on older, deformed sediments, fault blocks of Tertiary volcanics, and erosion surfaces on Precambrian crystalline rocks. The sedimentary sequence is composed of silts, inudstone, sands, gravels, limestone, gypsum, diatomite, and pyroclastic units. Previous investigations have designated these lithologies one unit, the Gila Conglomerate. A recent study in the Mammoth area (Heindi, 1963) subdivided the Gila Conglomerate into the Quiburis formation, Sacaton formation and Pleistocene to Recent alluvial deposits. In the present study, this nomenclature was utilized, with a proposed subdivision of the Quiburis formation. Detailed mapping of the lithologic units indicate a lateral facies change within the Quiburis formation0 The conglomeritic member of the Quiburis formation interfingers with a central, fine-grained member, and the names Tres Alasnos, and Redington are proposed for these units. The age of the Quiburis formation is based on its stratigraphic position, and vertebrate fossils. The Qulbuns ovenlies tilted sediments containing Miocene fauna, and its upper portions contain fauna which have been assigned a middle to late Pliocene Age. The Sacaton formation was deposited on an erosion surface in the Quiburis in late Pliobene to early Pleistocene time; it was then entrenched and local, middle to late Pleistocene lacustnine units were deposited in the drainage pattern. Fresh water mollusks, horse and mammoth remains are present in the lacusbnine units. The Pleistocene lacustrine units were truncated by late Pleistocene terraces, and degradation proceeded to approximately 80 feet below the present floodplain. Aggradation occurred, to a level above the present floodplain, as attested by prehistoric hearths buried in river sediments, above the present stream gradient. Since 1880 the San Pedro River has begun another period of downcutting. The sedimentary deposits control the movement of ground water in the valley. Two hydrologic systems are present; a shallow water table system in the floodplain and river channel area, and an artesian system at 630- 1,200 feet below the valley floor in the northern portion of the study area. It is believed that deformed, pre- Miocene sedinentary units provide the source of recharge to the artesian system. Detailed mapping of the sedimentary units reveals a meandering central trough of the ancestoral San Pedro River. The contact between the Redington and Tres Alamos members of the Quiburis formation indicate the meander pattern, and its control by bedrock outcrop. Structural activity continued through Pliocene time, and is represented by north trending normal faults. Minor slump structures and small reverse faults are present in the Redington member of the Quiburis formation. A site survey, carried out during the field mapping, resulted in the location of nineteen archaeological sites. The sites range from preceramic Desert Culture to Salado and probably to later cultures such as the Apache. Older sites are peripheral to the valley axis, with more recent sites concentrated along the river. It appears that geologic-hydrologic factors controlling site location are: water sources; agricultural or gathering areas; quarry, or source material sites; and vantage points.

Integrated geophysical methods, in combination with available well and geologic data, were used for the purpose of defining the subsurface hydrologic and geologic conditions beneath the Walnut Gulch Experimental Watershed and its peripheral area near Tombstone, Arizona. The 58-square mile watershed, within the 290-square mile area covered by portions of this study, was chosen by the U. S. Department of Agricuiture for intensive research relating to the water and sediment yields from a semiarid range land watershed, Surface geology of the watershed reveals an alluvial fandike area between igneous intrusive and sedimentary rocks that support the Tombstone gills o the southwest and the Dragoon Mountains on the northeast, An interface between the Cenozoic alluvium and volcanic rocks, and the igneous intrusive and sedimentary rocks which are noted as the basement complex, was based on velocity determinations from several seismic refraction profiles, and density determinations of 127 surface samples from 75 sites in 19 different formations, Average values of 2.26 gm/cm3 (grams per cubic centimeter) for the Cenozoic alluvium and volcanic rocks and 2.65 gm/cm3 for the intrusive igneous and sedimentary rocks established a density contrast across the interface of 0.39 gm/cm3, A network of 360 gravity stations established over the watershed and its peripheral area aided in defining configuration of the basement complex, provided depth approximations of the alluvium, and controlled the bearings for subsequent seismic traverses. Magnetic profiles over deep, alluvium-filled areas and the surrounding exposed bedrock was postulated to be useful in deducing source areas and depositional patterns within the alluvium. Structural control of groundwater flow to the northwest was suggested through a combined study of dominant trends on the gravity and magnetic maps. A gravity profile north of the watershed across the largest negative anomaly, with the regional gradient removed, was interpreted as an alluvium-filled graben having a width of ten miles, and a depth of 3500 feet east of its center. Toward the southeast, several parallel gravity profiles indicated a decrease in width and depth of the structure. A total of 54 seismic refraction profiles, aggregating a length of 120,000 feet of in-line seismic profiling, was conducted in 13 areas, Velocities derived from reversed seismic profiles, and profiles conducted over outcrops, averaged 2200 feet per second for channel fill, 5000 feet per second for unconsolidated alluvial deposits, 8800 feet per second for conglomerates, and depending on the particular unit, 12,300 to 15,600 feet per second for basement-type rocks. Mapping of the water table in many areas revealed depths from near zero at the confluence of Walnut Gulch and San Pedro River, to 475 feet in the central portion of the watershed. The accuracy of predicting the depth to either groundwater or basement was ± 6 percent, while that for groundwater alone was ± 10 percent. Analysis of the timedistance data, and correlations with surface geology, grayity, and well data provided a basis for the interpretation of the hydrogeology and recent alluvial history. Finally, a new application of velocities was used in this study to analyze a part of the hydrologic cycle. Based on 23 pairs of observation, a prediction equation was derived through linear regression analysis of density versus velocity. Using seismic velocities, the prediction equation, and relationships between density and porosity, areas of maximum transmission losses within the channel were estimated.

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